In communication, such as wireless communication, a technique for suppressing a peak of a transmission signal has been used for improving the electric power use efficiency of an amplifier. That is, the electric power use efficiency of the amplifier improves as the amplifier is operated close to saturation electric power. Thus, by suppressing a peak component of a signal through peak suppression in advance, the amplifier operates as close as possible to saturation electric power.
For example, a technique illustrated in FIG. 1 is known as a method of suppressing a peak and a method of restoring a suppressed peak. In this technique, a transmitter suppresses a peak, and then transmits peak suppression information related to peak suppression integrated with transmission data. Then, a receiver receives the peak suppression information, and then uses the received peak suppression information to restore the peak-suppressed signal (see Japanese Laid-open Patent Publication No. 2001-274768).
In addition, a peak suppressing method using hard clipping is known as a technique for suppressing a peak. Specifically, the peak suppressing method is a method in which a gain is determined so that a peak of a signal that exceeds a suppression target value is clipped to the target value. Note that as a technique related to hard clipping, a technique for suppressing a steep variation in a signal by applying a predetermined function to round the shoulder of the waveform after peak suppression (see FIG. 2) is known in order to suppress a steep variation in signal at a point at which suppression through hard clipping is started (see Japanese Laid-open Patent Publication No. 10-178414).
Here, in the technique for transmitting peak suppression information, the transmitter allocates a frequency for transmitting peak suppression information. As a result, there is a problem that frequencies that are allocatable to a user are reduced and, therefore, frequency use efficiency decreases.